1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus which magnetically records a digital data on a recording medium and reproduces the recorded digital data therefrom utilizing a helical scanning method, and particularly, to a magnetic recording and reproducing apparatus which can widen a playback speed range of special reproduction modes such as slow-forward and reverse play without a degradation of the reproduced data quality.
2. Description of the Prior Art
In a conventional magnetic recording apparatus such as a digital video tape recorder (DVTR) or a digital video cassette tape recorder (DVCR), wherein a head cylinder includes writing magnetic heads and reading magnetic heads, a recording tape is wrapped around the rotating head cylinder in a helical-shaped tape path for the recording and reproducing operations. The data is magnetically recorded on the recording tape by rotating the cylinder to scan recorded tracks with the writing head having a predetermined azimuth angle. The reading head with the same azimuth angle as that of the writing head scans the recording tracks that were scanned and recorded by the writing head just before to reproduce the recorded data therefrom. By arranging a pair of writing and reading heads having the same azimuth angle at a predetermined relational positions, the data recorded on the recording media can be reproduced from the recorded media at substantially the same time as the recording operation
However, the reading (reproducing) head scans across the tracks under the reverse-playback mode, because the data track extending direction is different from the reading (reproducing) head scanning direction. Therefore, the data obtained through every scanning are collectively stored in a memory, and are outputted as a video signal when the data in the memory becomes enough for one frame.
With reference to FIGS. 10, 11, 12, 13, and 14, an example of the conventional magnetic apparatus will be described in detail herebelow. As schematically shown in FIG. 10, a conventional magnetic apparatus CMA has mainly three functional system, a recording system, a head system Huc, and a reproducing system RSc that are constructed as shown therein.
In the recording system WS, a source analog signal Sv inputted through an input terminal 101 is digitized by a digital encoder 102 into an encoded source data Svd, and is further added with the error correction code by an ECC adder 103. Thus, a recording encoder 104 is constructed by the digital encoder 102 and the ECC adder 103 produces a recording data Sve in a digital format suitable for data exchange. This digitized recording data Sve is, then, modulated (Svm) and amplified (Sva) for the convenience of the recording process by the head unit HUc.
In the head unit Huc, a pair of reading/writing heads Rpa and Rpb and a pair of simultaneous reproduction (reading) heads Pa and Pb are provided in a circumferential side surface thereof such that each head pairs opposes each other, as best shown in FIG. 10. The writing (recording) heads Rpa and Rpb are used for writing the data Sva from the recording system WS to a recording tape TA wrapped therearound in a helical tape path and also for reading the data from the tape TA. The simultaneous reproduction (reading) heads Pa and Pb are used only for reproducing the data from the tape TA.
The reading/writing head Rpa and simultaneous reproducing head Pa are located with a predetermined positional relationship so that the head Pa can simultaneously reproduce the data from the track to which the head Rpa is just writing data, and are called a simultaneous reproduction head pair SHa. Similarly, another simultaneous reproduction head pair SHb is formed by the heads Rpb and Pb. The heads belonging to the same head pairs have the same azimuth angle, but are different form the azimuth angle of the other head pairs. Under the recording mode, the head unit Huc and tape TA are in the fixed directions indicated by arrows Dh and Dt, respectively. However, the tape TA can be fed in bilateral directions, or forwarding and reversing in direction Dt.
In the reproducing system RS, an reproducing amplifier 112c amplifies a data Sv read from the tape TA by either of heads RPa, RPb, Pa, and Pb to produce an amplified reproduction data SvP. A reproducing equalizer 114c equalizes the data SvP to produce an equalized data EvP. A reproducing demodulation 117c demodulates the equalized data Evp to produce a demodulated reproduction data Smc. An ECC corrector 121c performs an error correction of the demodulated reproduction data Smc to produce an error free demodulated reproduction data Svd. A digital decoder 122c decodes the reproduction data Svd to reproduce the original data Sv that will be outputted through an output terminal 124. Thus, the amplifier 112, equalizer 114c, and demodulator 117c construct a reproducing unit Rc which prepares the digital data Smc suitable for digital decoding process by a recording decoder 123c that is constructed by the ECC corrector 121c and the digital decoder 122c.
In FIG. 11, traces of head on the recording tape by the conventional magnetic recording and reproducing apparatus CMA under a slow-reverse playback mode wherein the data is reproduced at a reduced reproduction speed, or a half of the normal playback speed but the feeding direction is reversed, is shown. In this case, the tape TA is fed to the reversed playback direction -Dt, and the head is rotated in the fixed direction Dh. Several tracks formed on the tape TA are shown in rectangular shapes extending perpendicularly to the tape feeding direction Dt, each adjacent to each other. For the sake of brevity, only twelve tracks are discretely described with track numbers Tr1 to Tr-10 arranged in order along with the normal tape feeding direction Dt.
Slant arrows S1 to S10 in solid lines rising up diagonally to the left side inside the tracks TR 0 to TR-7 indicate traces of the head formed during the half-speed slow-reverse playback. Each of trace arrows S1 to S10 corresponds to a scanning by the simultaneous reproducing heads Pa and Pb alternately. FIGS. "1.1, 1.5, 1.9" and "-6.9, -6.5, -6.1" typically shown in the tracks TR1 and TR-7 respectively indicate the position on the corresponding tracks. For example, the integral number "-6" and fractional number "-0.9" of figure "-6.9" in the track TR-7 indicate the track No. and the linear position far from the track starting end. In this sense, these figures can be referred to as "an inter track position index". Specifically, the inter track position index is numbers not less than the track numbers TRn of the corresponding track, but less than TRn+1 of the next track. The simultaneous reproducing heads are constructed to have a track scanning width 1.28 times greater than that of the reading and writing heads such that they can reproduce the data from the target rack on which they scan at least two thirds area in the width of track.
In FIG. 12, a relationship between track scanning periods and the tracks from which the data can be reproduced under the half-speed slow-reverse playback mode of FIG. 11 are shown. Numbers, 0 to 10, shown in the horizontal axis TS each indicates a track scanning period SST required for a single head to scan one track on the tape TA under the normal playback mode at the scanning speed same as the data writing. Numbers, -1 to -5, shown in the vertical axis each indicates track number of corresponding tracks, and is located on a boundary distinguishing the corresponding track from the next track. For example, the track TR1 is described between the horizontal axes with 0 and -1.
As apparent from FIGS. 11 and 12, even in the conventional magnetic recording and reproducing apparatus CMA shown in FIG. 10 can reproduce the data from the tape keeping the continuity of track numbers in the range of slow-reverse playback speed from 0 to -1/2 of normal playback speed. Even though the head sometimes fails to read the data from the tracks scanned by themselves In other words, the data can be reproduced from every track, enabling a noiseless slow playback mode. Specifically, the data on the track TR-t can be reproduced fully by head tracings S8 and S10, as shown in FIG. 11. Under the noiseless slow playback mode means, full frame images can be reproduced at a reduced speed.
In FIG. 13, traces of head on the recording tape by the conventional magnetic recording and reproducing apparatus CMA under a slow-reverse playback mode, similar to those shown in FIG. 11 but the data reproduction is two thirds of the normal playback speed, is shown. In FIG. 14, a relationship between track scanning periods and the tracks from which the data can be reproduced under the half-speed slow-reverse playback mode of FIG. 13 are shown. As is apparent from FIGS. 13 and 14, the data on the track TR-5 can be intermittently reproduced by head tracings S6 and S8, disabling the noiseless slow playback. Thus, the reproducing speed enabling the noiseless slow playback is limited in the conventional magnetic recording and reproducing apparatus having simultaneous scanning head pairs.